1. Field of the Invention
The present invention relates to a wafer processing apparatus, a method of operating the same apparatus, and a wafer detecting system.
2. Description of the Related Art
When fabricating semiconductor devices on a semiconductor wafer (hereinafter referred to simply as xe2x80x9cwafersxe2x80x9d), the wafer is subjected to a heat treatment process in semiconductor device fabricating processes, such as a film forming process and an oxide film forming process. Such a heat treatment process is carried out by, for example, a heat treatment apparatus shown in FIG. 37. This heat treatment apparatus has a working region S1 in which an operator or an automatic carrying robot transports a wafer cassette, and a loading region S2 of an air cleanliness class higher than that of the working region S1. The working region S1 and the loading region S2 are separated by a wall 11, and a heat treatment furnace is installed in the loading region S2.
In this heat treatment apparatus, the loading region S2 is purged of the atmosphere with nitrogen (N2) gas to prevent the formation of an oxide film by natural oxidation, and is kept at a pressure higher than that in the working region S1 so that clean air flows from the loading region S2 into the working region S1 to prevent particles from entering from the working region S1 into the loading region S2. Therefore, nitrogen gas is supplied continuously at a fixed rate to the loading region S2 to maintain a fixed nitrogen concentration in the loading region S2. The pressure in the loading region S2 is regulated so that the pressure is higher than the atmospheric pressure by, for example, 1 Pa or above, preferably, about 100 Pa.
The use of a closed-type wafer cassette (hereinafter referred to as xe2x80x9cclosed-type cassettexe2x80x9d) 1 has been examined to suppress the contamination of wafers with particles (xe2x80x9cMonthly Semiconductor Worldxe2x80x9d, Jan., 1997). This closed-type cassette 1 has a cassette body 10 having a capacity of, for example, thirteen wafers W, and a lid 10a capable of hermetically closing an opening formed in the cassette body 10 to put the wafers W in and to take out the wafers W from the cassette body 10.
When using the closed-type cassette 1 in combination with the heat treatment apparatus, the closed-type cassette 1 is mounted on a cassette stand 12 disposed in the working region S1, and is fitted in an opening 11a formed in the wall 11 from the side of the working region S1. Normally, the opening 11a is closed by a door 13. A lid operating mechanism incorporated into the door 13 removes the lid 10a from the cassette body 10. Then, a door operating mechanism 15 for vertically and horizontally moving the door 13 carries the lid 10a together with the door 13 into the loading region S2. Then, a transfer mechanism 16 disposed in the loading region S2 and capable of vertically and horizontally moving and turning takes out the wafers W from the closed-type cassette 1 transfers the same to a wafer boat 17. Then, the wafer boat 17 is transported into a heat treatment furnace 18 to subject the wafers W to a predetermined heat treatment process.
Although the interior of the closed-type cassette 1 is purged with nitrogen gas, the pressure in the closed-type cassette 1 is about 1 atm (atmosphere), which is slightly lower than that in the loading region S2. Therefore, the pressure difference between the interior of the closed-type cassette 1 and the loading region S2 makes the lid 10a difficult to open, and hence the door operating mechanism needs a large power to remove the lid 10a from the cassette body 10 together with the door 13.
Since the pressure difference between the interior of the closed-type cassette 1 and the loading region S2 causes the gas to flow rapidly from the loading region into the closed-type cassette 1 of a pressure lower than that in the loading region S2, which may possibly produce particles.
The reliable detection of wafers W contained in the closed-type cassette 1 from outside the closed-type cassette 1 is convenient to the subsequent process for processing the wafers W.
The present invention has been made under such circumstances and it is therefore an object of the present invention to provide a wafer processing apparatus capable of smoothly opening the lid of a closed-type cassette having a wafer storage space of a pressure equal to or approximately equal to the atmospheric pressure in an atmosphere of a positive pressure in a loading region, a method of operating the same apparatus and a wafer detecting system.
According to a first aspect of the present invention, a wafer processing apparatus comprises: a loading region where a wafer is transferred from a cassette having a cassette body having an internal space to be kept at a pressure approximately equal to the atmospheric pressure, and a lid for closing an opening of the cassette body; a working region separated from the loading region by a wall provided with an opening; a cassette stand disposed at a position corresponding to the opening of the wall in the working region for supporting the cassette thereon; a lid operating unit disposed in the loading region for removing the lid from the cassette body; an inert gas supply passage provided with a valve for supplying an inert gas into the loading region; a cassette detecting unit provided at the cassette stand for detecting the cassette as mounted in place on the cassette stand; and a control unit for closing the valve of the inert gas supply passage on the basis of a signal from the cassette detecting unit, operating the lid operating unit to remove the lid from the cassette body and then opening the valve of the inert gas supply passage.
According to a second aspect of the present invention, a method of operating a wafer processing apparatus comprising a loading region where a wafer is transferred from a cassette having a cassette body having an internal space to be kept at a pressure approximately equal to the atmospheric pressure, and a lid for closing an opening of the cassette body; a working region separated from the loading region by a wall provided with an opening; a cassette stand disposed at a position corresponding to the opening of the wall in the working region for supporting the cassette thereon; a lid operating unit disposed in the loading region for removing the lid from the cassette body; an inert gas supply passage provided with a valve for supplying an inert gas into the loading region; a cassette detecting unit provided at the cassette stand for detect the cassette in place on the cassette stand; and a control unit for closing the valve of the inert gas supply passage on the basis of a signal from the cassette detecting unit, operating the lid operating unit to remove the lid from the cassette body and then opening the valve of the inert gas supply passage comprises the steps of: opening the valve to supply the inert gas into the loading region so as to set the loading region at a pressure not lower than the atmospheric pressure; mounting the cassette on the cassette stand, closing the valve of the inert gas supply passage on the basis of the signal from the cassette detecting unit and setting the loading region at a pressure substantially equal to the atmospheric pressure; removing the lid from the cassette body by the lid operating mechanism to open the interior of the cassette body into the loading region; and opening the valve of the inert gas supply passage to set the loading region at a pressure not lower than the atmospheric pressure.
According to a third aspect of the present invention, a wafer processing apparatus comprises: a loading region where a wafer is transferred from a cassette having a cassette body having an internal space to be kept at a pressure approximately equal to the atmospheric pressure, and a lid for closing an opening of the cassette body; a working region separated from the loading region by a wall provided with an opening; a cassette stand disposed at a position corresponding to the opening of the wall in the working region for supporting the cassette thereon; and a wafer detecting device disposed in the working region for detecting a wafer contained in the cassette from outside the cassette.
According to a fourth aspect of the present invention, a wafer detecting system comprises: a cassette for containing a wafer, having a cassette body having an internal space to be maintained at a pressure approximately equal to the atmospheric pressure and an opening, and a lid for closing the opening; and a wafer detecting device for detecting a wafer contained in the cassette from outside the cassette.